I did a series of tests and I found page load times to be practically identical between Firefox and Konqueror (measured on the basis of when the progress bars got to 100%). Konqueror had a slight edge on some sites (the BBC main page) whereas Firefox had an edge on others (redhat.com), but the difference was no more than a second or so.

Where Konqueror does have definite speed benefits is in the initial start-up time, and also when the browser hasn't been used for awhile - if I haven't used Firefox for an extended period of time, maybe half an hour or more, switching to Firefox takes forever (it takes about as long to revive as it does to start). By contrast, Konqueror is live within a second or so. Switching to "stale" tabs also seems faster in Konqueror.